In the metal extrusion arts there are known various extrusion presses for direct or indirect extrusion of a metal billet through an extrusion die. For example, in direct extrusion an elongated billet is held within a through bore in an extrusion container. A dummy block located at the front end of an extrusion stem is inserted into one end of the container bore and a powered ram moves the extrusion stem axially to force the contained billet through a stationary die located in a die carrier or die holder at the opposite end of the container bore. An elongated extruded member is thereby produced. This and other known extrusion operations commonly leave a waste portion of the billet, known as the butt, attached to the die face.
The prior art has provided various means for removing the butt end of a billet from the extrusion die. For example, U.S. Pat. No. 3,530,702 discloses an indirect loose die extrusion press including a cutoff saw which is utilized to separate a major extent of the extruded member from a stud end portion thereof whereby the extrusion is separated from the butt end of the billet. U.S. Pat. No. 3,563,079 discloses a combined direct/indirect extrusion press having a butt shear mounted on the forward platen thereof for shearing the billet butt end from the extrusion die.
The prior art of butt removal has been subject to certain shortcomings. Most significantly, the recent development of recessed weld pocket or feeder plate dies for aluminum extrusion has created a need for more reliable means for butt removal. These dies have a pocket or recess encompassing the extrusion opening on the billet side of the die. Thus, during extrusion operations the aluminum first flows into and fills the weld pocket. This permits a continuous extrusion process as the hot metal contained in the pocket after butt shearing rewelds with the next billet or initiation of the next extrusion cycle. This sort of process, which permits production of extrusions in continuous runs, is suitable only for extrusion of those aluminum alloys which will reweld as described. Other aluminum alloys, and other metals such as brass for example, will not reweld and in this manner therefore are not candidates for use of pocket weld dies.
Economy of cycle time is one primary objective of those extrusion operations which utilize pocket weld dies. Thus, such dies are often used in automated press lines, and often are provided with a number of extrusion openings for producing multiple extrusions from a single extrusion cycle. Accordingly, a die may have several weld pockets formed on its face.
Butt shears, when used in conjunction with such dies, exhibit a tendency to smear a film of the extrusion metal across the face of the die during butt shearing. This may result from misalignment between the die face and the shear blade and can cause undesirable delays in the extrusion operation. For example, for certain modes of shear blade to die face misalignment, a wedging action may result which wedges the shear blade tightly against the die face with hot aluminum from the billet filling the wedge gap between the shear blade and the die face. The shear blade may be so tightly wedged that even the full retraction force of the shear ram will be insufficient to free the shear blade.
Another more common problem associated with the shearing of a butt from a die face is the tendency of the butt to hang up on the shear blade rather than dropping free. Upon retraction of the shear blade, the hung up butt often will adhere to the die face as both the butt and film of metal smeared on the die face by the shearing operation will be quite sticky. Repetition of shear operation to dislodge the stuck butt often is unsuccessful and the butt may ultimately stick so firmly to the die face that extrusion operations must be interrupted to permit replacement of the die and stuck butt with a clean die.
Butt knockoff apparatus for forcefully dislodging a hung-up butt by striking same with an impact tool is known, but these too have been subject to certain shortcomings. For example, known knock-off apparatus, typically has been contained within in the perimeter of the shear actuating ram. This has resulted in unduly complex and difficult to maintain butt shear and knockoff arrangements. Furthermore, in prior butt knockoff structures the motion of the knockoff impact tool has been limited to motion along an axis parallel to the shear plane. This limitation has limited knocker utility as the hungup butt might well be located outside the path of travel of the butt knocker.